The overall goal of this research is to develop a better understanding of the mechanisms that underlie intensity processing in normal and impaired ears. A major portion of this proposal examines the relation between loudness growth and the ability to identify small increments in level, which is known as intensity resolution. Of particular interest are conditions that are known or ar likely to modify intensity resolution and loudness, such as adding tones to a complex tone or the detection of a brief tone during the onset oa a broadband noise (i.e., overshoot). Another phase of this research examines the relation between intensity resolution and loudness in individuals with acoustic tumors to test the hypothesis that adaptation is responsible for the abnormal intensity processing in these listeners. Subjects with acoustic tumors will enable a critical test of excitation-pattern models invoked typically for modeling intensity processing in normal and impaired hearing. A third series of experiments examines the role of cognitive factors (such as memory and context) on loudness and intensity resolution. Experiments with varied stimulus contexts (e.g., forward masking with cues) will provide data more relevant to everyday listening conditions than those from fixed stimulus contexts, but both fixed and variable contexts need to be studied to separate cognitive mechanisms from sensory ones. This proposed research will provide critical tests of current models for relating loudness and intensity resolution and should provide insights into the mechanisms underlying these phenomena. The data from these experiments also should prove useful in the design and fitting of hering prostheses, such as in the evaluation of channel independence in cochlear implants.